Printed circuit board assembly with improved bypass decoupling for BGA packages

Abstract

A printed circuit board assembly with improved bypass decoupling for BGA packages. In one embodiment, a capacitor may be interposed between a BGA package and a PCB within a perimeter of the contact pads that form a BGA footprint. The capacitor may have physical dimensions which allow a BGA package to be mounted such that there is no physical contact between the capacitor and the BGA.

What is claimed is:  
     
       1. A printed circuit board assembly comprising: 
       a printed circuit board (PCB), wherein said PCB includes a plurality of contact pads which forms a ball grid array (BGA) footprint;  
       a BGA package having a plurality of contacts electrically connected to said plurality of contact pads;  
       a capacitor interposed between said PCB and said BGA package;  
       wherein said plurality of contact pads are located on a first surface of said PCB, and wherein said capacitor is connected to additional contact pads located on said first surface of said PCB; and  
       wherein said BGA and said capacitor are mounted to a common substantially planar surface of said PCB.  
     
     
       2. The printed circuit board assembly as recited in  claim 1 , wherein said additional contact pads are located within an area defined by a perimeter of said BGA footprint. 
     
     
       3. The printed circuit board assembly as recited in  claim 2 , wherein said capacitor is a leadless capacitor. 
     
     
       4. The printed circuit board assembly as recited in  claim 3 , wherein said capacitor is contained within a capacitor package. 
     
     
       5. The printed circuit board assembly as recited in  claim 4 , wherein said capacitor package includes a first capacitor and a second capacitor. 
     
     
       6. The printed circuit board assembly as recited in  claim 5 , wherein said first capacitor and said second capacitor have different capacitance values. 
     
     
       7. The printed circuit board assembly as recited in  claim 6 , wherein capacitance values of said first capacitor and said second capacitor differ by a factor of 10. 
     
     
       8. The printed circuit board assembly as recited in  claim 3 , wherein said capacitor is no more than 0.5 millimeters in thickness. 
     
     
       9. The printed circuit board assembly as recited in  claim 3 , wherein said capacitor has a tolerance of ±20%. 
     
     
       10. A method for providing decoupling capacitance for a ball-grid array (BGA) package including a plurality of electrical contacts, the method comprising: 
       mounting a capacitor on a printed circuit board (PCB), wherein said PCB includes a plurality of contact pads which forms a ball grid array (BGA) footprint;  
       mounting said BGA package to said PCB, wherein said electrical contacts are electrically connected to said plurality of contact pads, wherein said capacitor is interposed between said BGA and said PCB, and further wherein said BGA and said capacitor are mounted to a common substantially planar surface of said PCB.  
     
     
       11. The method as recited in  claim 10 , wherein said plurality of contact pads are located on a first surface of said PCB, and wherein said capacitor is connected to additional contact pads located on said first surface of said PCB. 
     
     
       12. The method as recited in  claim 11 , wherein said additional contact pads are located within an area defined by a perimeter of said BGA footprint. 
     
     
       13. The method as recited in  claim 12 , wherein said capacitor is a leadless capacitor. 
     
     
       14. The method as recited in  claim 13 , wherein said capacitor is contained within a capacitor package. 
     
     
       15. The method as recited in  claim 14 , wherein said capacitor package includes a first capacitor and a second capacitor. 
     
     
       16. The method as recited in  claim 15 , wherein said first capacitor and said second capacitor have different capacitance values. 
     
     
       17. The method as recited in  claim 16 , wherein capacitance values of said first capacitor and said second capacitor differ by a factor of 10. 
     
     
       18. The method as recited in  claim 13 , wherein said capacitor is no more than 0.5 millimeters in thickness. 
     
     
       19. The method as recited in  claim 13 , wherein said capacitor has a tolerance of ±20%. 
     
     
       20. A printed circuit board assembly comprising: 
       a printed circuit board (PCB), wherein said PCB includes a plurality of contact pads which forms a ball grid array (BGA) footprint;  
       a BGA package having a plurality of contacts electrically connected to said plurality of contact pads;  
       a capacitor interposed between said PCB and said BGA package;  
       wherein said plurality of contact pads are located on a first surface of said PCB, and wherein said capacitor is connected to additional contact pads located on said first surface of said PCB; and  
       wherein said capacitor is no more than 0.5 millimeter in thickness.  
     
     
       21. The printed circuit board assembly as recited in  claim 20 , wherein said additional contact pads are located within an area defined by a perimeter of said BGA footprint. 
     
     
       22. The printed circuit board assembly as recited in  claim 20 , wherein said capacitor is a leadless capacitor. 
     
     
       23. A printed circuit board assembly comprising: 
       a printed circuit board (PCB), wherein said PCB includes a plurality of contact pads which forms a ball grid array (BGA) footprint;  
       a BGA package having a plurality of contacts electrically connected by soldering material to said plurality of contact pads;  
       a capacitor interposed between said PCB and said BGA package;  
       wherein said plurality of contact pads are located on a first surface of said PCB, and wherein said capacitor is connected to additional contact pads located on said first surface of said PCB; and  
       wherein said capacitor is no thicker than the height of the soldering material.  
     
     
       24. The printed circuit board assembly as recited in  claim 23 , wherein said capacitor is no more than 0.5 millimeters in thickness. 
     
     
       25. The printed circuit board assembly as recited in  claim 23 , wherein said additional contact pads are located within an area defined by a perimeter of said BGA footprint. 
     
     
       26. The printed circuit board assembly as recited in  claim 23 , wherein said capacitor is a leadless capacitor.